Electrically conductive polymers represented by polythiophene, polypyrrole, polyaniline and the like are a group of compounds that have been actively developed in the field of “organic electronics” recently. In the subject field, substances having conductivity in the range from about 10−2 to about 10−6 S/m are generally used as antistatic agents, static removing agent and the like.
Among such electrically conductive polymers, particularly, a polyaniline is obtainable from inexpensive raw materials, and a polyaniline is one of the first electrically conductive polymers that are in practical use. Thus, polyaniline that does not have any substituents is used as electrically conductive material. In order to cause polyaniline that does not have any substituents to achieve conductivity, however, it is necessary to perform doping (also referred to as dope) treatment with an acceptor or a donor with proton, iodine or the like, and such polyaniline itself that does not have any substituents does not have conductivity. Moreover, polyaniline that does not have any substituents is generally insoluble in solvents, and it is thus difficult to be shaped into a desired form, thus having a problem of poor workability.
In order to solve such a problem of a polyaniline that does not have any substituents, polyanilines, which are obtained by introducing a long chain alkyl group, ketone group, ether group or the like into polyaniline, with improved solubility against organic solvents have been reported. In the present specification, unless otherwise stated, the term “polyaniline” refers to both those that do not have any substituents and those that have substituents.
In addition, with regard to productivity, cost and the like in producing and shape processing of polyaniline, it is desirable for polyaniline to be water soluble. Thus, polyanilines with given water solubility have been recently developed by introducing an acidic substituent having proton into polyaniline. Furthermore, with regard to such polyaniline to which an acidic substituent is introduced, when the acidic substituent is introduced, the proton of the acidic substituent is doped. Thus, there is an advantage of obtaining conductivity without the need of performing a doping process separately (which is referred to as self-dope or self-doping). With regard to the acidic substituent herein, those in which a sulfo group (—S(O)2OH) or phosphonic acid group (—P(O)(OH)2) is used are known. Some of them are developed or expected in the use for prevention of static charge due to their conductivity.
As to polyaniline to which a sulfo group is introduced, “those obtained by sulfonating unsubstituted polyaniline with fuming sulfuric acid or chlorosulfuric acid” (Patent Document 1) and “those obtained by polymerizing aniline-sulfonic acids” (Patent Document 2) are known. In the method of performing sulfonation as described in Patent Document 1, a greatly excess amount of sulfonation agents are used for polyaniline to perform sulfonation, and a large amount of acidic waste is produced, resulting in a problem of difficulty in the disposal thereof. The method using aniline-sulfonic acids as described in Patent Document 2 has a problem of high product cost due to the high price of the raw material.
With regard to polyaniline having a phosphonic acid group, a method of polymerizing o-aminobenzylphosphonic acid to obtain poly(o-aminobenzylphosphonic acid) has been reported (Non-Patent Document 1). With this method, however, multiple stages of reaction are required to obtain a raw material that is used for polymerization. Specifically, a step of allowing o-bromomethyl-nitrobenzene (Br is present in Compound 1 in Scheme 1 on page 8518 of Non-Patent Document 1, and thus the description of “o-methylnitrobenzene 1” on page 8518, left column, 9th line from the bottom is a typographical error) to react with triethyl phosphite to obtain diethyl o-nitrobenzylphosphonate 2 (hereinafter, referred to as step 1); a step of reducing the diethyl o-nitrobenzylphosphonate 2 with cyclohexane to obtain diethyl o-aminobenzylphosphonate 3 (hereinafter, referred to as step 2); and a step of hydrolyzing the diethyl o-aminobenzylphosphonate 3 with concentrated hydrochloric acid to obtain o-aminobenzylphosphonic acid 4 (hereinafter, referred to as step 3) are performed to obtain a monomer that is used for polymerization. Furthermore, purification must be performed at each reaction, and thus there are many industrial problems to be solved from the viewpoint of productivity. In detail, it is necessary to perform reaction with 3 steps to obtain a raw material prior to polymerization, and including the polymerization, it is necessary to perform reaction of 4 steps. In Non-Patent Document 1, the yield and purification method of the respective steps are as follows: step 1: 64% (purification using column chromatography), step 2: 71% (purification using ion exchange), step 3: 65% (purification using recrystallization), and step 4 (polymerization): 30%.
As described above, various studies have been conducted for polyaniline; and with regard to the technique of allowing polyaniline to have an acidic substituent, sulfo groups are mainly studied as the acidic substituent. With regard to the technique of introducing a phosphonic acid group, those skilled in the art do not pay a lot of attention on it because the technique has some disadvantages such as complication of the producing steps, and no active studies have been conducted therefor. In particular, no studies have been conducted for the use of aniline monomers having a structure in which a phosphonic acid group is directly bound to a benzene ring.
Now, with regard to the mechanism of a polymerization reaction of aniline monomers as well as the structure of polyaniline, and the mechanism of expressing the conductivity, while there are some parts that have not been completely clarified, a variety of studies have been conducted and a variety of findings have been discovered.
For example, Yano et al., BUNSEKI KAGAKU Vol. 46, No. 5, pp. 343-349 (Non-Patent Document 2), Japanese Laid-Open Publication No. 2003-192786 (Patent Document 3), J. Stejekal et al., Progress in Polymer Science 35 (2010) 1420-1481 (Non-Patent Document 3) and Mukai et al., Keio University Hiyoshi Kiyou, Shizen Kagaku (The Hiyoshi review of the natural science), No. 50 (2011.9), p. 61-75 (Non-Patent Document 4), describe the mechanism of a polymerization reaction of aniline monomers.
Furthermore, Hino et al., Yamagata University Kiyou (engineering), Vol. 29, No. 2, February, Heisei-19 (Non-Patent Document 5) describes the mechanism of an oxidative polymerization of polyaniline and the structure of polyaniline obtained by an oxidative polymerization. Specifically, it is described that: a structure with conductivity referred to as an emeraldine salt is formed by an oxidative polymerization, and when the emeraldine salt is treated in an alkaline solution, an insulating structure referred to as emeraldine base is formed; when the emeraldine base is reduced, a structure referred to as leucoemeraldine is formed; and when the emeraldine base is oxidized, a structure referred to as pernigraniline is formed.
It is a well-known fact that polyaniline takes such four types of structures; and for example, Japanese Laid-Open Publication No. 2004-99673 (Patent Document 4), Japanese Laid-Open Publication No. 2008-33203 (Patent Document 5), and Japanese National Phase PCT Laid-open Publication No. 2011-501379 (Patent Document 6) describe the above-mentioned four types of structures.
It should be noted that while reactions in which phosphite is caused to bind with a benzene ring in the presence of a catalyst such as a palladium compound are publicly known (Non-Patent Documents 6 to 10), such reactions are solely studied for the purpose of developing a method for introducing a substituent into a benzene ring, and these reactions have not been known to be used for synthesis of polymers.